Film drive compensatory mechanism



June 16, 1953 R. w. WENGEL. 2,641,961

FILM DRIVE COMPENSATORY MECHANISM Filed April 21, 1952 2 Sheets-Sheet 1RAYMOND W. WENGEL INVENTOR.

ATTORNEY & AGENT June 16, 1953 R. w. WENGEL FILM DRIVE COMPENSATORYMECHANISM 2 Sheets-Sheet 2 Filed April 21, 1952 INVENTOR.

RAWOND w. WENGEL ATTORILIE'Y.AGENT Patented n 16.1953

FILM DRIVE (JOMPENSATOR Y MECHANISM:

Raymond W. Wengel, Rochester, N. Y., assignor to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey Application April 21,1952, Serial No. 283,297

Claims.

This invention relates to photographic apparatus and more particularlyto a mechanism associated with the advancing means for a film strip inwhich the driving and holding points of spaced driving members arecompensated or varied in accordance with the length of the film striptherebetweemthe difference in length of the film strip being due toeither shrinkage or stretch thereof.

As is well-known in the photographic art, a film strip may shrink orstretch depending on the conditions under which the film is stored orhandled. Inphotographic apparatus used in I conjunction with television,the film used in either a cameraor projector must be properly registeredat the film gate and the errors of registration must be reduced to aminimum. In m copending U. S. application, Serial No. 196,152, which wasfiled November 17, 1950, a pull-down mechanism is disclosed in which thefilm is registered and advanced by means of air under pressure appliedto the loops of film ahead of and beyond the film gate. Such a pull-downarrangement permits accurate registration of the film at the apertureand accomplishes pull-down of the film strip in a time interval which isequivalent to a 7-8 degree shutter sector and to the retrace interval ofa television tube. It has been found, however, that any shrinkage orstretch of the film strip very seriously hampers proper registration andallowance must be made in the pull-down cycle for the time required bythe usual sprocket arrangement to advance the film a distance equal tothe maximum amount of shrinkage to be expected in a length equal to theloop or to retract an amountof film equivalent to the maximum amount ofstretch. The time lost'in this way may be as much as five times thetotal time available for a 7-8 degree pulldown.

The present compensatory mechanism has been developed as an essentialfactor in minimizing the errors of position of the film perforationsrelative to the locating pin arising from variations in the film stripdue to shrinkage orlstretch. With the usual sprocket and locating pin,the locating pin is arranged so at the end of the pulldown stroke theperforation is positioned to engage the pin without interference, thisassumes, of course, that the film is of standard or normal length. Withshrunk film the perforation would be stopped short of engagement and acertain amount of time, which would be in proportion to the shrinkage,would be needed to feed. the film downward until engagement with thelocating pin could occur. By driving the sprocket ahead of its normalpositionin accordance with the shrinkage, the present invention alwayspositions the perforation in a position to engage the register ing pinat the end of the pull-down stroke. The primary object of the invention,therefore, is to provide in a photographic apparatus a mechanismassociated with the film sprocket for moving the film strip toward thefilm gate which will advance or retard movement of the sprocket inaccordance with the amount of shrinkage or stretch in the film stripwhereby registration of each image area at the film gate is properlyaccomplished. Y

Another object of the invention is to provide me photographic apparatusa drive mechanism including a differential gear train for coupling andimparting rotation to a pair of spaced film engaging members and forvarying, in accordance with the length of film between said members, therelation of the driving point of one of said members to the holdingpoint of said other member. V

Still'another object of the invention is to provide in a photographicapparatus a drive mechanism including a planetary gear train forcoupling and imparting rotation to a pair of spaced film engagingmembers and for varying, in accordance with the length of film betweensaid members,'the relation of the driving point of said one memberwithrespect to the holding point of said other member in the same ratio asthe lengths of film between the registering means at the film gate andthe holding and driving points of said members.

Yet another-object of the invention is to provide in a photographicapparatus a pair of spaced film engaging members, one of said membersbeing a. driving member and the other a holding member, arranged aheadof the film gate and havingdriving and holding points, respectively,which are spaced at substantially the same distanceirom each other asthe driving point is from the registering means at the film gate, saidmembers being coupled together and rotated through a planetary geartrain which, in accordance with. the length of film between saidmembers, varies the relation of the driving point ofv said one memberwith respect to the holding. point of said other member to maintain saiddriving point substantially equidistant from said registering. means andsaid holding point.

. A further object of the invention is to provide I in rt-photographicapparatus a mechanism associated. with the film sprocket for moving thespaced film engaging members, one of said mem here being a drivingmember and the other a holding member arranged ahead of the film gateand having driving and holding points, respectively, which are spaced atsubstantially the same distance from each other as the driving point .is

spaced from the registering means at the film gate, said members beingcoupled together and intermittently rotated by a Geneva mechanismincluding a planetary gear train which, in accordance with the length offilm between said members, varies the relation of the driving point withrespect to the holding point so it is substantially equidistant fromsaid registering means and the holding point, the film strip andintermittently driven members of the drive being clamped during theinterval the film is stationary at the film gate.

These and other objects and advantages will be apparent to those skilledin the art by the description which follows. 1

Reference is now made to the accompanying drawings wherein likereference numerals designate like parts and wherein: v

Fig. 1 is a diagrammatic side elevation of a motion picture projectorshowing the relative positions of the film gate, film locating pins, airchambers and rotary valves together with the drive means forcontinuously moving the film strip towardthe film gate;

Fig. 2 is a perspective view, partly in section, showing the drive meansfor coupling the sprockets and for varying the relation of the drivingand holding points of the sprockets in accordance with the length offilm therebetween;

Fig. 3 is a diagrammatic detail view of a film strip showing therelation of the registering pin to the driving and holding points of thesprockets;

Fig. 4 is a perspective view, partly in section, showing anotherembodiment of the invention in which the film is moved intermittentlyand the film strip and sprockets are automatically clamped during theinterval the film is station- Y;

Fig. 5 is, a detail end view of the brake member on the holding sprocketshaft;

Fig. 6 is a detail end view of the shoe for-clamping the film on theholding sprocket;

Fig. 7 is a vertical section through a resilient clamping device adaptedto be arranged between the sprockets; and

Fig. 8 is a vertical section taken substantially on line 88 of Fig. 7.

The present invention is shown in Fig. 1 as adapted to a projector formotion picture film which is used in conjunction with a televisiontransmitting and/or receiving device and which utilizes air underpressure applied to the film loops for registering and advancing thefilm strip, the diagrammatic representation being that of the preferredembodiment shown and described in my above-mentioned U. S. patentapplication.

As described in said application, the film strip F 4 with an aperturell, by Sprocket l2 to form a loop between sprocket l2. and gate 10. Thefilm strip between sprocket l2 and gate I0 is maintained in a loop byair under pressure which is admitted to chamber l3 by rotary valve 14.

The means for registering each image area on the film strip withaperture H comprises pin l5 which is arranged adjacent -aperture H andhas a fixed surface against which an edge of the film perforation isheld by the air applied against the upper loop. While only one pin maybe used, it has been found that two spaced :pins definitely insureproper registration of the image areas adjacent 2. splice in the filmstrip. A second chamber I6 is located below the film gate and isenclosed by the film strip being moved therethrough. Rotary valve Hadmits air under pressure to chamber 16 in timed relation to that ofvalve l4. Sprocket l8 which is continuously rotated moves the film stripfrom the lower loop to the take-up reel. 7 a

If it is assumed the film strip has just been advanced, at such instantthe film strip will be taut between pin [5 and sprocket l2 in chamber l3and formed in a loop between gate l0 and sprocket l8 in chamber l6..Valve [4 then admits air under pressure to chamber I3 and as sprocket[2 moves film toward gate It, the air pressure maintains said film in aloop and, at the same time, maintains the edges'of the film perforationsagainstthe surface of pin l5 for holding the film strip in registrationat aperture H. At this time, the air pressurein chamber 16 is cut off byvalve H and spr0cket;l8 is mcvin the film strip from chamber 16 towardthe take-up reel, thereby reducing the lower loop. When the air pressurein chamber I3 is cut off by valve l4, Valve I! then admits air tochamber [6 and the air under pressure introduced into chamber 16 causesthe lower film loop to expand, thereby moving the film ofit pin 15andadvancing it until the next perforation is opposite pin l5 at whichtime the film will again be taut between sprocket l2 and pin l5. Thefilm strip is, therefore, advanced and registered by air :pressureapplied alternately and in timed relation to the film loops on each sideof the film gate. the foregoing description relates to one of theembodiments disclosed in my copending application for advancing andregistering a film strip, the present invention about to be described isapplicable to any type of photographic or other apparatus in which astrip material which is subject to shrinkage or stretch must beaccurately measured or registered at a point intermediate two fixedstations.

From the foregoing description, it can be readily appreciated that anyshrinkage or stretch in the film strip willseriously disruptregistrationof each image area at film gate 10. In order to eliminate the error inregistration which is due to shrinkage or stretch, a drive means hasbeen devised which will automaticallyv compensate sprocket I2 for anychanges in the length of the film strip. This is accomplished byproviding an auxiliary sprocket 20 on shaft 2! which is positionedbetween sprocket l2 and the supply reel, not shown. A drive means isalso provided which couples and imparts rotation to both sprockets formoving the film strip toward gate Ill. 7 Sprockets l2 and 20 arearranged so that the distance from pin l5 to the driving point ofsprocket I2 is substantially equal to the distance between the driving,point of sprocket l2 and the holding point of-sprocket 2D. a

While- The driving point of sprocket l2is defined as the region in whichthe forward or working surface of a sprocket tooth is in engagement withthe leading edge of a film perforation to move the film strip. Theholding point of sprocket 2|) is defined as the reg-ion in which therear surface of a sprocket tooth corresponding to that of sprocket I2 isin engagement with the trailing edge of a film perforation to maintainthe film taut between the sprockets. In the event rollers are used inplace of sprockets, the driving and holding points would then be theregion through which the rollers engage the film strip to move it towardthe gate. With reference to Fig. 3 it will be noted p designates thepitch of the film perforation. In the case of 16 mm. film an image areaor frame is located between adjacent perforations so that n will thendesignate the number of image areas between pin l5 and a tooth |2d onsprocket l2 and between tooth |2d and a corresponding tooth 20h onsprocket 20, and 1m will designate the pitch of the film perforationstimes the number of perforations. Although pin l5 and tooth |2d engagethe leading edge of the perforations, the forces acting on the filmstrip are in opposed directions, that is, the force of the air pressureon the film loop tends to maintain the leading edge of the perforationagainst pin [5 and the trailing edge of the perforation against tooth20h. The force exerted on tooth |2d to drive the film into the loop isalso against the leading edge of the perforation to overcome thefriction applied to sprocket 20 as described hereinafter. Since theworking surface of tooth |2d engages the leading edge of the filmperformation to drive the film toward gate l and the rear surface oftooth 20h engages the trailing edge of the perforation to maintain thefilm between said teeth taut, the forces exerted on the film strip bythe teeth of the sprockets are also opposed.

In the assembly of the device, it is necessary to assemble the sprocketswith corresponding teeth on each sprocket engaging the perforations asjust described. Inasmuch as the sprocket teeth do not contact or engageboth edges of the perforations, the front surface of tooth 20h will bespaced a distance 1m +C from the front surface of tooth |2d, C being theclearance or difference between the width of the sprocket tooth andwidth of the perforation. If the number of image areas between pin l andtooth |2d is the same as those between tooth |2d and tooth 2011., theactual difference in dimension will be only clearance C, provided thefilm is free of any shrinkage or stretch so that for allpracticalpurpose the distances are substantially equal. As a result eachperforation is positioned opposite pin l5 and aligned therewith so thatany variation in the length of the film between corresponding teeth ofthe sprockets will result in improper positioning of any perforationwith respect to pin I5.

The error in positioning each film perforation with respect to pin I5 isminimized or eliminated by providing a drive means which comprises wormwheel 25 which is integral with sleeve 26 and freely rotatable therewithby means of bearings 21 on shaft 28 to which sprocket l2'is secured, agear 29 fixed to shaft 28 by pin 30, and a pair of gears 3| and 32 whichare also freely rotatable on shaft 28 by reason of bearings 33. Thedrive means also includes a worm 34 on shaft'35 which is driven by amotor, not shown, a pair of pinions 36 and 31 secured to stub shaft 38which is journaled in bearing'sleeve 39 formed-integral with sleeve 26and-rotatable'therewith, an idler gear 40 on shaft 4|, and a gear 42secured to shaft 2| to which sprocket 20 is also secured.

Sprocket I2 is the compensatory sprocket whose rotation is to bechanged. Auxiliary or holding sprocket 20 is coupled to sprocket I 2through the gear train comprising gears 42, 40 and 32, the differentialor planetary gear train 3 I, 31, 36 and 29 and bearing sleeve 39.Consequently, as the motor drives worm 34, worm wheel 25 and sleeve 26are rotated, the bearing sleeve 39 being rotated with sleeve 26 andcarrying pinions 36 and 31 therewith. As the pinions are carried aboutshaft 28, pinion 36 which meshes with gear 29 fixed to shaft 28 causesgear 29 and, hence, shaft 28 and sprocket H to be rotated. In a likemanner, pinion 31 meshes with gear 3| to rotate it and gear 32 onbearings 33 and through idler gear 40, which meshes with gears 32 and42, rotates gear 42 and, hence, shaft 2| and sprocket 20. If bearingsleeve 39 is regarded as being stationary and gear 42 isrotated in theforward direction through some angle, idler 40 will be rotated and causegear 32 to also be rotated in the forward direction carrying with itgear 3| which imparts rotation to gears 36 and 3'! so that finally gear29, shaft 28 and sprocket |2 are also rotated together in a forwarddirection. It is evident that the action of the. differential shortensthe distance between the driving and holding points of the sprocketsbecause of the gear ratio in the differential and, conversely, if gear42 is rotated in the opposite direction, the distance will be increased.This action is independent of the rotation of the system as a wholesince the drive is through the bearing sleeve 39 or sleeve 26 of thedifferential. Sincethe driving point of sprocket I2 is positionedsubstantially equidistant from pin l5 and the holding point of sprocket20, the movement of sprocket |2 with respect to sprocket 20 must be inthe same ratio as the lengths of film between pin l5 and the driving andholding points of the sprockets. Accordingly, since the film lengths aresubstantially equal, the overall ratio of the differential must be 2:1so that sprocket I2 is rotated through only one-half the angle ofsprocket 20. Therefore, if sprocket I2 is positioned at any other pointalong the film strip between pin l5 and sprocket 20, the differentialratio will of necessity have to be changed and will be in the same ratioas the ratio of the film lengths.

If sprockets I2 and 20 are coupled by some other means in addition tothe differential gearing, such as film F, the sprockets are free toassume any phase relation made necessary by such coupling. Thus, thedriving and holding points of the sprockets may be positioned toproperly engage theirrespective perforations irrespective of anyshrinkage or stretch in the film and the driving point of sprocket I2will be advanced, relative to its normal position, a distance equivalentto the shrinkage in the film between the driving and holding points ofthe sprockets with the result that a speed of pull-down equivalent tothe retrace time of a television scanning system can be sion of the filmbetween sprockets l2 and 20 would be approximately fifty per centgreater than thetension dueto the pull of the supplyreel and would varyas the pulls and jerks of theisupply reel change the torque applied tothe sprocket by the film. To'overcome this condition and to isolate themechanism from such disturbances, an additional sprocket .05 ispositioned between sprocket 20 and the supply reel, sprocket 45 feedingthefilm into a loop L from which the filmis fed toward the gate bysprockets I 2 and 20. Loop L can be put under tension by applyingan airstream or air under pressure to said loop to supply the necessaryresisting torque.

A uniform and controlled tension in'the film between sprockets I2 and'20 is also required in order to maintain the perforation edges incontact with the forward or working faces of the sprocket teeth. Such aretard or tension means comprises a friction pad 33 on a resilient arm41 which is biased toward gear 42 so that pad 40 engages the face ofsaid gear. Since the sprockets are coupled by the gear anddifferentialmechanism, the necessary friction couldbe applied as well togear 32 or gear 00. Other forms of mechanical resistance could also beused, such as viscous resistance, eddy current damping, etc. In anycase, the tension developed in the film must be sufficient to overcomethe natural tendency of the film to spring out of a straight pathbetween sprockets l2 and 20 and to withstand the jerk of the pull-downstroke so that the film is not pulled away from the teeth of sprocketlz.To assist in maintaining the film strip, in engagement with thesprockets and against the face'of film gate I0, hold-down rollers 48,40, 50 are utilized, as is well-.- known in the art.

In Fig. 4 another embodiment of the invention is disclosed in which thefilm strip is advanced intermittently and sprockets I2 and 20 arearranged so that the film strip is moved under sprocket 20 and oversprocket I2. Shaft I is driven by a motor not shown and through helicalgears HM and I02 drives shaft I03 continuously. Shaft I03 is journaledin bearing I00 and has fixed thereto a cam I05 and a collar I06 whichcarries drive pin I0? for star wheel I08 of the Geneva mechanism. .Starwheel I08 is freely rotatable on shaft 2| and carries a stud I09 onwhich th integral pinions 36 and 3'I are journaled and are freelyrotatable. Pinion 38 meshes.

with gear 29 fixed to shaft EI, and pinion3l' meshes with gear 3i whichis integralwith gear 32, gears 3| and 32 being freely rotatable'on shaft2|. Shaft 28 and sprocket I2 are rotated by gear I I0 which is fixed toshaft 20 and meshes with gear 32.

As described with respect to the first embodiment, the intermittentrotation of starwheel I08 by pin I0l, which is accomplished'in awellknown manner, is transmitted through pinion 36 and gear 29 to shaft2I and through pinion 31, gears 3i and 32 and gear I I0 to shaft 28,sprockets I2 and 20 being rotated in'opposite directions because of therelation of the sprockets to the film strip. Any shrinkage or stretchofthe film will, therefore, alter the driving point of sprocket I2 withrespect to the holding point of sprocket 20. This action is independentof the rotation of, the system as a whole, since the drive is throughstar wheel I08 and the differential.

During the interval that pin I01 is driving wheel I08 and shafts 2| and20 through the .differential, brake member III is acting as a dragonshaft 2!. Brake member III, see Figs. 4 and 5, comprises a cylindricaldrum II2 whichlis secured to shaft 2I and a brake'band I I3 having anextension lsld which is anchored to bearing. I04 by pin I I5 sothat band,I I3 cannot rotate with shaft 2i and a forward extension IIB which isintermittently engaged by cam I05 to clamp shaft 2| against. rotationduring the idle period of wheel I08. The fixed pin I I5 may be replacedby an adjustable stop (not shown) to provide an easy control of thefrictional resistance caused by the; brake band. The use of anintermittent drive and clamp, as described above, insures that whileadesirable amount of frictional resistance is present duringthe'rotationof the sprockets to produce the necessary tension in thefilm between them, yet when the pull-down stroke occurs, the system isrigidly clamped, so that the pullof the film cannot rotate the sprocketsand spoil the registration of the perforations at locating pin I5.

In Fig. 4 is shown a supplementary film clamping device to be usedwhenthe forces actingon the film'are not only strong enough to disturbthe operation of the differential drive but are too great for thestrength of the erforations engaging teeth of the sprockets I2 and 20.Such a clamping device comprises a shoe I20 which is pivotally mountedon stud I2I and retained between plates I22 which are pivotally mountedon shaft I03 or a suitable stub shaft connected to shaft I03 by means ofa suitable gear train. Shoe I20 extends a short way around sprocket 20in the direction of rotation and terminates in a suitably curved portionwhich cooperates with cam. I 23 fixed on shaft I03, That part of theshoe which wraps the sprocket is curved in such a way that when theoperation of cam I23 brings shoe I20 closer to the sprocket, thepressure feet I24 nearest the axis of stud I2I are first brought intocontact with the film on the sprocket and then are followed byadditional pairs of feet in the order of their distance from said axis,see Fig. 6. A sufficient number of pressure feet is used to provide thedesired holding power. The working'surfaces of feet 124 are suitablyrelieved to avoid scratching the film in the image or sound track areasand to provide clearance for the passage of the sprocket teeth. Also,feet I24 are positioned to work in the spaces between sprocket teethwith the gaps centered on the teeth and are of suitable width toinsurethat the feet will not clamp on a film splice, as shown in Fig. 6-

PlatesJI22 and shoe I20 are retainedin an operative position withrespect, to sprocket 20 by the detent I25. When detent I25 is withdrawnfrom the aperturein wall I26, th unit maybe swung down about shaft I03against a stop not shown to provideclearance for threading the ,film..An undercut roller.I2'I is freely rotatable onistud I2I and when in theoperative position, revents the film from engaging plates I22 or anyother part of the sprocket clamping assembly. It is understood thatsuitable hold-down rollers and a pull-off sprocket are also utilized asshown in- Fig. 1 and described with respect to the first mentionedembodiment, v 7

As alternative arrangements for clamping and/or guiding the film strip,a resiliently mounted member I30 is movably mounted with respect to wallI3 I, as shown in Figs. 7 and 8, and with the movable member I32provides a guidewayfor the film strip between sprockets I2 and 20,-Asshown in Fig. 8, members I30 and I32 are suitably undercut in .amannerand for purposes well-known in the art. Member I32 is moved againstmember I30 by'cam I33 which is secured to shaft I34. A suitable geardrive, not shown, connects shaft I 34 with shaft I03. Leaf spring I35 ismade sufficiently strong to insure proper clamping of the film strip andat the same time must permit splices to be moved between said members.Such a structure will serve to edge guide the film strip during movementthereof, to clamp the film strip when it i stationary, and to dampen anywaves set up in the film strip by the extreme speed of the pull-down.Such a structure in which member I 32 is fixed and member I30 isresiliently mounted as shown may be used in conjunction with thesprocket film clamping device for guiding and damping the film strip,the spring I35 then being made very light since its sole purpose will beto maintain the film in position and to accommodate for any splices.

With the mechanism described hereinbefore, the sprocket I2 isautomatically driven ahead of its normal position in accordance with theamount of shrinkage, or may lag behind its normal position if the filmis stretched, so that the perforation at the'film gate will alwaysbe inposition to engage the locating pin at the end ofthe pull-down stroke.While the present mechanism is described with reference to a motionpicture projector, it is applicable to many other type of apparatus inwhich a strip material is subject to shrinkage or stretch. The drivingsprockets l2 and 20 can be rollers which frictionally drive the stripmaterial and the differential mechanism may take many difierent forms.Also, the film strip may be advanced and registered by other means thanthose disclosed. and described above. Since many other modifications ofthe invention will be suggested to those skilled in the art, the scopeof the present invention is not to be limited in any respect by thepresent disclosure but is defined in the appended claims.

Having now particularly described my invention, what I desire to secureby Letters Patent of the United States and what I claim is:

1. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, of film driving members arranged ahead of saidfilm gate and including a compensatory driving member having a drivingpoint and an auxiliary driving member having a hold-back point and formoving said film strip toward said film gate, the compensatory drivingmember being arranged be tween said film gate and said auxiliary drivingmember, and drive means including a differential gear train foroperatively coupling and imparting rotation to said film driving membersand for varying, in accordance with the length of film between said filmdriving members, the relation of the driving point of said compensatorydriving member with respect to the hold-back point of said auxiliarydriving member.

; 2. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,of film driving members arranged ahead of said film gate and including acompensatory driving sprocket having a driving point and an auxiliarydriving sprockethaving a hold-back point and for moving said film striptoward said film gate, the compensatory driving sprocket being arrangedbetween said registering means and said I auxiliary driving sprocket,and drive means including a planetary gear train for operativelycoupling and imparting rotation to said film driving members and forvarying, in accordance with the length of film between said film drivingmembers, the relation of the driving point of said compensatory drivingsprocket with respect to the hold-back point of said auxiliary drivingsprocket in the same ratio as the lengths of film between saidregistering means and said driving point and said hold-back point.

3. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,of film driving members arranged ahead of said film gate and including acompensatory driving sprocket having a driving point and an auxiliarydriving sprocket having a holdback point and for moving said film striptoward said film gate, the compensatory driving sprocket being arrangedbetween said registering means and said auxiliary driving sprocket,drive means including a planetary gear train for operatively couplingand imparting rotation to said film driving members and for varying, inaccordance with the length of film between the driving point andhold-back point of said sprockets, the relation of the driving point ofsaid compensatory driving sprocket withjrespect to the hold-back pointof said auxiliary driving sprocket in the same ratio as the lengths offilm between said registering means and the driving point and holdbackpoint of said sprockets, and retard means associated with said drivemeans for maintaining the film strip between said sprockets undertenslon.

4. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said film gate, of film driving members arranged ahead ofsaid film gate and including a compensatory driving member and anauxiliary driving member both for moving said film strip toward saidfilm gate, the compensatory driving member being arranged between saidauxiliary driving member and said film gate and having a driving pointsubstantially equidistant from the upper edge of said aperture and aholdback point of said auxiliary driving member, and drive meansincluding 'a differential gear train for operatively coupling andimparting rotation to said driving members and for varying, inaccordance with the length of film between said film driving members,the relation of' the driving point and the hold-back point of said filmdriving members to maintain the driving point of said compensatorydriving member substantially equidistant from said edge of said apertureand the hold-back point of said auxiliary driving member.

5. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said film gate, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,of a pair of film driving members arranged ahead of said film gate andincluding a compensatory driving sprocket and an auxiliary drivingsprocket both for moving said film strip toward said film gate, thecompensatory sprocket being arranged between said auxiliary sprocket andsaid film gate and having a driving point substantially equidistant fromsaid registering means and a hold-back point of said auxiliary sprocket,and drive means including a planetary gear train for operativelycoupling and imparting rotation to said. sprockets and for varying, inaccordance with the length of film between said sprockets, the angularrelation of said driving point to maintain the driving point of saidcompensatory sprocket substantially equidistant from said registeringmeans and the'hold-back point of said auxiliary sprocket.

6. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past saidfilm-gate, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,of a pair of film driving members arranged ahead of said film gate andincluding a compensatory driving sprocket and an auxiliary drivingsprocket both for moving said film strip toward said film gate, thecompensatory sprocket being'arranged between said auxiliary sprocket andsaid film gate and having a driving point substantially equidistant fromsaid registering means and a hold-back point of said auxiliary sprocket,drive means including a planetary gear train for operatively couplingand imparting rotation to said sprockets and for varying, in accordancewith the length of film between'said sprockets, the angular relation ofsaid driving'and hold-back points to maintain the driving point of saidcompensatory sprocket substantially equidistant from said registeringmeans and the hold-back point of said auxiliary sprocket, and retardmeans associated with said drive means and said auxiliary drive sprocketfor maintaining the film strip between said sprockets under tension.

'7. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said film gate, and registering means arranged adjacent saidaperture for positioning each image area with respect. tov saidaperture, of a pair of film driving members arranged ahead of said filmgate and including 'a'compensatory drivin sprocket and an auxiliarydriving sprocket both for moving said film strip toward said film gate,the compensatory sprocket being arranged between said auxiliarysprocket. and said film gate and having a driving point substantiallyequidistant from said registering means and a hold-back point of saidauxili'arysprocket, and drive means including a planetary gear: trainfor operatively coupling and impartingrotation to said sprockets and forvarying, in accordance with the length of film between said sprockets,the angular relation of the driving point and hold-back point ofsaidsprockets, the driving point of said compensatory sprocket beingmoved through substantially one-half the angular movement of thehold-back point of said auxiliary sprocket to maintain the driving'pointof said compensatory sprocket substantially equidistant from saidregistering means and the'holdv back point of said auxiliary sprocket.

8. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,

of film'driving members arranged. ahead of: said 12 film gate andincluding a drive shaft, a compensatory driving member secured to saiddrive shaft and having a driving point, an auxiliary drive shaft and anauxiliary driving'member secured to said auxiliary drive shaft andhaving a hold? back point, both film driving members being adapted tomove said film strip toward said film gate and with the compensatorydriving member being arranged between said auxiliary driving member and'saidfilm gate, a drive means ineluding. a worm wheel and a pair ofcoaxially aligned gears freely rotatable on. said drive shaft, a gearsecured to said drive shaft, a second gear secured to said auxiliarydrive shaft, an idler gear operatively connecting said second gear andone of said pair of gears, and a pair of coaxially aligned pinionscarried by said worm wheel for movement around said drive shaft, one ofsaid pinions meshing with said gear and the other of said pinionsmeshing with the other of said pair of gears for operatively couplingand imparting rotation to said film driving members and-for varying, inaccordance with the length of film between the. driving point andhold-back point of said film driving members, the relation of thedriving point of said compensatory driving member with respect to thehold-back point of said auxiliary driving member in the same ratio asthe lengths of film between: said. registering means and the drivingpoint and the holding point of said'film'driving members.

9. In photographic apparatus. havinga film gate provided with anaperture, the combination with a film advancing means for" moving'a filmstrip past said aperture, and registering means arranged adjacent saidaperture forpositioning each image area with respect to said aperture,of film driving members arranged ahead of' said film gate and includinga drive shaft, a compensatory sprocket secured to said drive shaft, anauxiliary drive shaft and an auxiliary sprocket secured to saidauxiliary drive shaft, both sprockets being adapted to move said filmstrip toward said film gate and with said compensatory sprocket beingarranged between said auxiliary sprocket and said film gate and having adriving point substantially equidistant from said registering'means anda hold-back point of said auxiliary sprocket, a drive means including aworm wheel and a pair of coaxially aligned gears freely rotatable onsaid drive shaft, a gear secured to said. drive shaft, 'a second gearsecured to said auxiliary drive shaft, an idler gear operativelyconnecting, said second gear and one of said pair of gears and a pair ofcoaxially aligned pinions carried by said ,wormwheel for movement aroundsaid drive shaft, one of said pinions meshing with said. gear and theother. of said pinions meshing with the other of said pair of gears foroperatively coupling and imparting rotation to said sprockets and forvarying, in accordance with the length of film between the driving andhold-back points of said sprockets, the relation of the" driving andhold-back points of said sprockets to maintain the driving point of saidcompensatory sprocket substantially equidistant from said registeringmeans and the hold-back point of said auxiliary sprocket.

10. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, and registering means arranged adjacent saidaperture for. positioning each image area w-ithyrespect to saidaperture,

of film driving members arranged ahead of said film gate and including adrive shaft, a compensatory sprocket secured to said drive shaft, anauxiliary drive shaft and an auxiliary sprocket secured to saidauxiliary drive shaft, both sprockets being adapted to move said filmstrip toward said film gate and 'with said compensatory sprocket beingarranged between said auxiliary sprocket and said film gate and having adriving point substantially equidistant from said registerin means and ahold-back point of said auxiliary sprocket, a drive means including aworm wheel and a pair of coaxially aligned gears freely rotatable onsaid drive shaft, a gear secured to said drive shaft, a second gearsecured to said auxiliary drive shaft, an idler gear operativelyconnecting said second gear and one of said pair of gears, and a pair ofcoaxially aligned pinions carried by said worm wheel for movement aroundsaid drive shaft, one of said pinions meshing with said gear and theother of said pinions meshing with the other of said pair of gears foroperatively coupling and imparting rotation to said sprockets'and forvarying, in accordance with the length of film between the driving andhold-back points of said sprockets, the relation of the drivin andhold-back points of said sprockets to maintain the driving point of saidcompensatory sprocket substantially equidistant from said registeringmeans and the hold-back point of said auxiliary sprocket, and retardmeans frictionally engaging said second gear for maintainin the filmstrip between said sprockets under tension.

11. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, of film driving members arranged ahead of saidfilm gate and including a compensatory driving member having a drivingpoint and an auxiliary driving member having a hold-back point and formoving said film strip toward said film gate, the compensatory drivingmember being arranged between said film gate and said auxiliary drivingmember, and drive means including an intermittently driven member and adifferential gear train movable thereby for operatively coupling andimparting intermittent rotation to said film driving members and forvarying, in accordance with the length of film between said film drivingmembers, the relation of the driving point of said compensatory drivingmember with respect to the hold-back point of said auxiliary drivingmember.

12. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, of film driving members arranged ahead of saidfilm gate and including a compensatory drivin member having a drivingpoint and an auxiliary driving member having a hold-back point and formoving said film strip toward said film gate, the compensatory drivingmember being arranged between said film gate and said auxiliary drivingmember, and drive means including an intermittently driven member and adifferential gear train movable thereby for operatively coupling andimparting intermittent rotation to said film driving members and forvarying, in accordance with the length of film between said film drivingmembers, the relation of the driving point of said compensatory drivingmember with respect to the hold-back point of said auxiliary drivingmember, and means responsive to said drive means for pre- 44 ventingmovement: of said film 'during'the in terval' the' film strip isstationary.-

' 13.In':photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip'past said'film gate, of film driving members arranged ahead ofsaid film gate and including a compensatory driving member and anauxiliarydriving member-:bothfor moving said film strip toward said filmgate, the compensatory driving member being arranged between saidauxiliarydriving memberand said film gate and having a driving pointsubstantially equidistant from the upper edge of said aperture and aholdback point of said auxiliary driving member, drive means includingan intermittently driven member and a differential gear train carriedthereby for operatively coupling and imparting rotation to said drivingmembers and for varying, in accordance with the length of film betweensaid film driving members, the relation of the driving point and thehold-back point of said film driving members to maintain the drivingpoint of said compensatory driving member substantially equidistant fromsaid edge of said aperture and the hold-back point of said auxiliarydriving member, and braking means normally producing a drag on saidauxiliary driving member and operatively connected to said drive meansand actuated thereby for preventing rotation of said film drivingmembers during the in: terval the film strip is stationary.

14. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,of film driving members arranged ahead of said film gate and including acompensatory driving sprocket and an auxiliary driving sprocket both formoving said film strip toward said film gate, the compensatory sprocketbeing arranged, between said film gate and said auxiliary sprocket andhaving a driving point substantially equidistant from said registeringmeans and a holdback point of said auxiliary sprocket, drive meansincluding an intermittently driven member and a differential gear trainmovable thereby for operatively coupling and imparting intermittentrotation to said sprockets and for varying, inaccordance with the lengthof film between said driving and hold-back points of said sprockets, theangular relation of said driving and holdback points to maintain thedriving point of said compensatory sprocket substantially equidistantfrom said registering means and the hold-back point of said auxiliarysprocket, and means responsive to said drive means for preventingmovement of said film strip and said film driving members duringinterval the film strip is stationary.

15. In photographic apparatus having a film gate provided with anaperture, the combination with a film advancing means for moving a filmstrip past said aperture, and registering means arranged adjacent saidaperture for positioning each image area with respect to said aperture,of film driving member arranged ahead of said film gate and including acompensatory driving sprocket and an auxiliary driving sprocket both formoving said film strip toward said film gate, the compensatory sprocketbeing arranged between said film gate and said auxiliary sprocket andhaving a driving point substantially equinewer 15 16 distant from saidregistering-means and a hold- 'terval the film strip is stationary, andmeans'ara differential gear train movable thereby for upfilm stripagainst movement during the interval eratively coupling and impartingintermittent ro- 5 the filmv strip is stationary.

tation to said sprockets and for varying, in accordance with the lengthof film between said RAYMOND W. WENGEL. driving and. hold-back points ofsaid sprockets, 1 the angular relationof said driving and hold-References Owed m the file 0f thls p tent back points to maintain thedriving. pointof said 10 v UNITED. STATES PATENTS compensatory sprocketsubstantially equidistant from said registering means and the hold-backig ag i E Name r J i g point of said auxiliary sprocket, braking means gaf -'1" 1951 normally producing a drag on said film driving fi e 3 5members and operativel y connected to said drive 15 W g; g 2 1952 means:and actuated, thereby for preventing rota- 2,601,790 Magnusson July19.52

tion of: said film drive members during the inback point of saidauxiliary sprocket, drive means ranged adjacent said film drivingmembers. and. including an intermittently'driven member and responsiveto said drive means for clamping said.

